PHP 8 reference · String Functions

PHP md5() Function

Calculate the MD5 hash of a string as 32 hex characters. Fine for checksums and cache keys, never for passwords.

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Syntax

md5(string $string, bool $binary = false): string

Parameter	Description
`string`	The input string.
`binary` optional	`true` returns the raw 16-byte digest. Default: `false`

The hash as a hex string.

Hash a stringTry it yourself

<?php
echo md5("hello"), "\n";
echo strlen(md5("hello")), "\n";

Output

5d41402abc4b2a76b9719d911017c592
32

A cache keyTry it yourself

<?php
$cacheKey = "user-list-" . md5(json_encode(["page" => 2, "sort" => "name"]));
echo $cacheKey, "\n";

Output

user-list-3320cd749d441ea9581e5d59a7a70438

Never store passwords with md5() or sha1(). Use password_hash() and password_verify().
MD5 is broken for security uses (collisions are easy). Prefer hash("sha256", …) for integrity checks.

Version	Change
PHP 4.0	Added

sha1() · Calculate the SHA-1 hash of a string as 40 hex characters. Weak for security; prefer hash("sha256", ...).
hash() · Hash a string with the algorithm you choose, such as sha256, sha512, crc32b or xxh3. Returns a hex string.
base64_encode() · Encode binary data or text as Base64, using only letters, digits, + and /, so it travels safely as text.
PHP Strings · tutorial

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